Several instrumental techniques will be used to study lateral and rotational motions of membrane molecules involved in lymphocyte stimulation by antigens and in luteal cell activation by gonadotropins. Fluorescence photobleaching recovery (FPR) and image-intensified video microscopy (IIVM) examine molecular lateral motions while polarized fluorescence depletion (PFD) measures protein rotational relaxation. B lymphocytes decorated by a new technique with artificial antigen receptors exhibit polyclonal differentiative responses to specific antigens. The lateral and rotational mobilities on these cells of bound antigens, antigen receptors, integral membrane proteins and lipid probes will be measured. Results will be compared with data on natural antigen-specific cells to better understand the role of surface immunoglobulin in B cell activation. Membrane dynamic requirements for B cell presentation of T-dependent antigen to T helper cells will be investigated. The role of B cell Ia and accessory cell proteolytic processing of antigen should be clarified by these studies. Mathematical models for antigen interaction with cell surface receptors will be extended and their predictions tested against experimental data. Binding of various gonadotropins such as luteinizing hormone (LH) and human chorionic gonadotropin to LH receptors on luteal cells will be examined by FPR and PFD. This will show how mobilities of hormone-receptor complexes are related to the duration of progesterone responses. The initial distribution, hormone-induced redistribution, and sites of internalization of LH receptors will be sought by electron microscopy and by IIVM to assess the connection between receptor redistribution and luteal cell activation. LH receptor mobility will be artificially restricted by crosslinking to test whether changes in receptor dynamics actively affect luteal cell steroidogenic responses to gonadotropins. Instrumental facilities for FPR, PFD, and IIVM will be updated and expanded.